Mercury screen centrifugal separator

ABSTRACT

A centrifugal separator for and a method of recovering highly divided value particles, principally gold and platinum, having a greater specific gravity than mercury. A relatively shallow and large-diameter bowl is provided with a mercury retention channel formed in and extending substantially the entire vertical height of the vertical side wall of the bowl and positioned at a predetermined distance from the point of joinder between the side and bottom walls of the bowl. The retention channel is formed in one embodiment with upper and lower horizontal faces and a vertical bottom face, and in a second embodiment with a sloping bottom face giving the channel greater depth at the bottom. The separator bowl is rotated at a speed sufficient to stabilize the mercury screen within the retention channel forming a smooth substantially vertical face over which the value-containing material is caused to pass in a substantially vertical path. The mercury wall or film within the channel acts as a screen through which particles of greater specific gravity than mercury are caused to pass by centrifugal force to cover the bottom face of the retention channel thereby displacing the mercury. The value particles thus collected are primarily finely-divided oxide and sulfide-coated gold particles and particles of platinum. The mercury screen does not flow but is stabilized or immobilized and is only removed by erosion as the bottom face of the channel builds up with the separated value particles. The mercury eroded from the channel face is washed off and recovered.

United States Patent [191 Gilkey 1 May 15, 1973 [54] MERCURY SCREEN CENTRIFUGAL SEPARATOR {76] Inventor: Walter W. Gilkey, PO. Box 505,

Mount Vernon, Wash. 98273 22 Filed: Mar. 7, 1969 211 Appl. No.: 805,317

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 611,683, Jan. 25,

1967, abandoned.

Primary ExaminerWilliam 1. Price Attorney- Seed, Berry and Dowrey [5 7] ABSTRACT A centrifugal separator for and a method of recovering highly divided value particles, principally gold and platinum, having a greater specific gravity than mercury. A relatively shallow and large-diameter bowl is provided with a mercury retention channel formed in and extending substantially the entire vertical height of the vertical side wall of the bowl and positioned at a predetermined distance from the point of joinder between the side and bottom walls of the bowl. The retention channel is formed in one embodiment with upper and lower horizontal faces and a vertical bottom face, and in a second embodiment with a sloping bottom face giving the channel greater depth at the bottom. The separator bowl is rotated at a speed sufficient to stabilize the mercury screen within the retention channel forming a smooth substantially vertical face over which the value-containing material is caused to pass in a substantially vertical path. The mercury wall or film within the channel acts as a screen through which particles of greater specific gravity than mercury are caused to pass by centrifugal force to cover the bottom face of the retention chan nel thereby displacing the mercury. The value particles thus collected are primarily finely-divided oxide and sulfide-coated gold particles and particles of platinum. The mercury screen does not flow but is stabilized or immobilized and is only removed by erosion as the bottom face of the channel builds up with the separated value particles. The mercury eroded from the channel face is washed off and recovered.

3 Claims, 3 Drawing Figures PATENTED 1 51975 3,732,979

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' WALTER w. GILKEY I, 1 IO lNVENTOR ATTORNEYS 1 MERCURY SCREEN CENTRIFUGALSEPARATOR This is a continuation-in-part application of my co- BACKGROUND OF THE INVENTION The present invention relates in general to centrifugal separators and more particularly to a centrifugal separator and a method for recovering ore values having a higher specific gravity than mercury by causing them to pass through a screen of mercury. by centrifugal force.

Throughout the history of placer gold mining, no method or apparatus has been devised for positively capturing the flake, flour or microscopic-sized gold and other valuable metals contained in the fine sands. Since very little of this size particle is recovered by present methods, the amount of values lost to tailings is not generally appreciated. As the placer areas containing the heavier gold are depleted, commercial operations must move out into the valleys where contained gold values are principally flake, flour or microscopic-sized particles. Even with the best present-day jigs and amal-.

gamators, the large yardage volume which must'be handled and the amount of recovery for the volume handled make these operations economically very marginal or not workable at all.

In addition to flake, flour and microscopic gold particles which are not commercially being recovered, the problem is compounded by the fact that a large percentage of the gold particles is coated with oxides and sulphides which, like platinum, have no affinity for mercury and thus will not amalgamate. Some applica tion of force is therefore necessary in order to physi cally separate the fine value particles from the sands.

In the prior art, separation by force has been accomplished by using centrifugal separator bowls which have rectangular mercury retention chennels in their vertical walls within which liquid mercury is suspended by the centrifugal force created by rotation of the bowl. The tailings or waste materials containing the value particles are directed upwardly within the bowl past the mercury screen. The dense value particles penetrate the mercury screen and are trapped within the channel while the less dense waste material continues upwardly out of the bowl. However, these prior-art separators have proven unsatisfactory because of the excessive loss of mercury due to erosion. The tailings erode the mercury screen as they pass over the screen and not all the mercury leaving. the bowl with the tailings is recoverable. Furthermore, the bowl must be stopped to replenish the supply of mercury, thereby losing valuable operating time. This is significant because the separators are commonly operated in the continuous production line of a gravel yard, mining operation or the like and require prolonged operation periods to prove economically successful.

According to the present invention, fine particles and even microscopic value particles are separated and retained by the application of centrifugal force using the specific gravity of mercury as a medium of separation. The present invention provides a screen of mercury in liquid form which is stabilized or immobilized within a retention channel of new and improved design. Experiments have shown that the erosion of the mercury screen is substantially prevented by positioning the lower surface of the retention channel above a vertical rise portion three-sixteenths inch or less extending from the lower surface of the channel to the tangent point between the bottom and side walls of the bowl. Likewise, experiments have shown that if the vertical rise portion is greater than three-sixteenths inch, the mercury in the channel is rapidly eroded since the mercury has a tendency to coat the longer vertical rise portion, thus presenting a fine film of mercury that is particularly susceptible to erosion by the granular materials passing over it. It is believed that the use of a vertical rise portion greater than three-sixteenths inch triggers a rapid erosion of the mercury in the channel as the adhering mercury is carried away by the first tailings fed into the bowl. Consequently, the improved design of the present invention includes an optimum vertical rise spacing of substantially one-eighth inch to prevent erosion of mercury.

In addition to the critical positioning of the retention channel, the construction of separator bowls is improved by sloping the bottom surface of the retention channel rather than utilizing a rectangular retention channel taught by the prior art. It is believed that the sloping bottom surface of the retention channel prevents erosion because it provides additional volume near the bottom of the retention channel for holding mercury seeking the lower levels because of gravity. By providing this additional volume within the channel near the bottom, the mercury is prevented from flowing or sagging out of the channel into the path of the tailings'.

Another significant feature of the present bowl construction is the fact that its diameter is relatively large compared to itsheight whereas the prior-art separator bowls have been of generally smalll-diameter with relatively high side walls. The present design simplifies construction of the bowl and allows a reduction in the weight of separator bowls.

The primary object of the present invention is, therefore, to provide a mercury screen centrifugal separator of the character described and a method for positively recovering extremely fine and microscopic size value particles by the application of centrifugal force and the medium of a mercury screen.

It is another object of the present invention to improve the efficiency of the centrifugal separator bowl. Specifically, it is an object to prevent or minimize the erosion of mercury by positioning the retention channel at a critical location within the bowl.

Still another object of the present invention is to prevent erosion of mercury from the retention channel of a separator bowl by increasing the depth of the retention channel atthe bottom relative to the top to keep the mercury from extending into the path of the tailings.

Other and more particular objects and advantages of the present invention will be apparent to those skilled in the art from the following specification and appended claims and from the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of the separator apparatus;

FIG. 2 is a partial vertical cross-sectional view of the separator bowl portion of the device; and

FIG. 3 is an enlarged cross-sectional view ofa second embodiment for the retention channel of the present invention.

DESCRIPTION OF THE INVENTION The separator comprises a separator bowl of a specific cylindrical formation, the details of which will be presently described and which is supported for axial rotation within a stationary double-walled cylindrical casing indicated generally at 11. The casing 11 includes an outer wall 12, laterally-spaced inner wall 13 and a base 14. The space between the walls 12 and 13 provides an annular channel 16 for the removal of waste sand and water after the values have been removed in the bowl 10 as will presently be described. A spirallydirected downwardly inclined trough member 17 is located between the walls 12 and 13 for directing the waste to an outlet spout 18 for discharging the waste material.

The waste material discharges from the spout 18 into a mercury recovery pan 19 provided with rotary agitators 21 driven by the motor 22 in a conventional manner. The pan 19 serves to allow any mercury which is eroded from the mercury screen to settle and separate from the flowing sand and water which is finally drained off by the drain boards 23.

The casing 11 is provided with a removable cover 24, the outer periphery of which is fitted with a flexible deflector member 26 which may be a sheet of rubber or the equivalent secured to the flange 27 carried by the cover. The deflector 26 serves to direct the waste material flowing over the top edge of the bowl downwardly into the trough 16. The casing 11 is also provided with a supporting wall 28 on which is mounted the bearing block 29 for journaling the upper end of the rotatable drive shaft 31. The shaft 31 is provided with a hub 32 centrally located within the casing for mounting the bowl 10 for rotation within the inner wall 13 of the casing. The bottom end of the shaft 31 is received in a bearing 33 mounted on the case 14. A drive motor 34 is also carried on the base and is connected to rotate the shaft 31 by means of the drive belts 36 trained about the drive wheel 37 on the motor shaft and the driven pulley 38 on the lower end of the shaft 31. Although an electrical motor 34 and a belt drive is illustrated, it will be obvious that any equivalent means for rotating the drive shaft 31 at the desired speed may be utilized.

The top cover 24 is provided with an opening in the central portion thereof defined by the flange 39 for receiving an inlet chute and distributor pan. The inlet chute is in the form of a cylindrical pipe 41 connected to a conical distributor pan 42 which extends downwardly into the bowl 10 as illustrated in FIG. 2. The bottom end of the chute 41 is provided with vertical slots 43 to allow the sand or ore concentrate and water to flow downwardly over the top surface of the pan 42. The outer periphery of the pan 42 is bent upwardly to form a vertical flange 44 spaced inwardly from the vertical side wall of the bowl 10. The outer edge portion of the pan 42 is provided with spaced holes 46 to allow the material to be washed out of the pan and onto the bottom of the separator bowl. Since the ore is mixed with water, in an approximately 3 to 1 weight ratio, i.e. 3 parts water to 1 part sand by weight, the material will be washed across thesurface of the pan in all directions and downwardly to the outer edge where is is allowed to drop downwardly onto the separator bowl. The chute 41 and distributor pan 42 are supported on the top cover 24 by means of the radial support arms 47 which may be connected by any suitable means to the chute 41 and which rest on the top surface of the cover 24.

Water is introduced into the chute 41 through an inlet pipe 48 suspended centrally within the chute 41 by means of the spanners 49. The sand is introduced into the water stream through the pipe 51. The bottom end of the pipe 48 may be provided with a screen 50.

Referring now to the bowl portion of the separator, shown in detail in FIG. 2, the bowl is mounted for rotation within the casing walls 13 and is fixed to the rotating hub 32. As aforementioned, one feature of the present bowl construction is its characteristic of being relatively shallow and of a relatively large diameter as compared with the prior art concept of deep, smalldiameter separator bowls. Although different sizes of separator bowls are feasible according to the present invention. Bowls suitable for field use have been constructed using a bowl diameter of approximately 36 inches and with an overall depth of only 7 inches. The bowl has a vertical side wall 52 with an outwardlyturned flange 53 for mounting an annular rim 54, the purpose of which will be presently described. The bottom end of the vertical wall 52 is provided with a shoulder 56 which, in the present preferred embodiment, is formed by reducing the thickness of the wall of the bowl. In the present example and with the bowl size previously mentioned, the depth or horizontal width of the shoulder 56 may be in the range of one-eighth inch to three-sixteenths inch. The annular rim 54 extends inwardly from the top edge of the wall 52 forming a second. shoulder 57 which will be identical in horizontal width to the shoulder '56. It will be realized, of course, that other forms of construction may be used in order to provide the upper shoulder 57. In this first embodiment of the invention, the lower horizontal surface formed by the lower shoulder 56 and the upper horizontal surface formed by the upper shoulder 57 cooperate with the vertical surface 58 to form a rectangular mercury retention channel which serves to confine the stabilized mercury screen. In practice and with the bowl dimensions given, the vertical height of the face 58 may be in the range of 4% inches to 5 inches with this dimension being determined by the vertical height at which a thin wall of mercury may be stabilized which, in turn, depends upon the rotational speed of the bowl.

As indicated in FIG. 2, the vertical wall 52 extends a slight distance below the lower shoulder 56 forming a vertical rise portion 59 immediately below the lip of the shoulder 56. This vertical rise section in the present embodiment will be in the nature of one-eighth inch and is highly important to the proper functioning of the separator as will presently be explained. The bottom wall of the bowl is a curved wall portion 61 having a rather gentle curve from the hub 32 outwardly and upwardly and rather sharply curving into the bottom of the vertical wall portion 59. As indicated by 0 in the drawings, the vertical distance between the low portion in the center of the bowl and the bottom of the vertical rise portion 59 is termed the radial rise of the bowl and, in the present instance, is approximately 2% inches.

In operation, according to the present method, the bowl will be rotated with a rim speed of approximately 2,050 feet per minute which has been determined to be satisfactory for stabilizing a vertical wall of mercury of approximately A; inch depth and at the previouslymentioned 4 /2 inch to 5 inch vertical height within the channel formed by the upper and lower horizontal surfaces 56 and 57 and the vertical face 58 of the bowl. In order to establish the mercury wall or screen, mercury is merely fed into the rotating bowl and will climb and fill the retention channel. The mercury thus presents a. substantially vertical face and completely fills the retention channel where it remains stationary as: long as the bowl is rotated so as to maintain thel proper centrifugal force.

With the mercury screen stabilized, value-bearing sand or other ore is then introduced into the bowl through the pipe 51 with water being introduced through the pipe 48. Although there is a certain natural range within which the bowl will function, a minimum ration of 2 parts water to 1 part sand by weight is required, the greater amount of water making erosion of the mercury less likely. As the value-bearing material is distributed through the holes 46 in the pan 42, the material falls into the bottom of the bowl and is driven outwardly by centrifugal force and upwardly by the radial rise 0 of the bowl bottom. In order to prevent erosion it has been found essential to deflect the material into a substantially vertical path parallel to the vertical face of the mercury screen before it passes the mercury and for this reason, the vertical rise portion 59 is provided. Without a definite vertical rise portion 59, the sands would be deflected into the face of the mercury and would gradually erode the mercury and prevent recovery. In addition, the specific dimension of the vertical rise 59 has been shown by experiment to be critical. When the vertical rise 59 exceeds three-sixteenths inch, the mercury is eroded from the retention channel shortly after the first quantity of sand is fed into the bowl. It is presently believed that a small quantity of mercury adheres to the vertical rise while the retention channel is being filled and when this quantity is carried away by the sand, it triggers the rapid erosion of the mercury in the channel. By reducing the dimension of the vertical rise below three-sixteenths inch, mercury will not be retained on the vertical rise 59. In particular, a vertical rise 59 of one-eighth inch has given excellent results.

The erosion of mercury is reduced even further by employing the novel channel configuration of FIG. 3. The retention channel 70 of this embodiment is also spaced a distance of three-sixteenths inch or less above the tangent point 71 between the surfaces 72 and 73 of the side and bottom walls 74 and 75, respectively. The preferable spacing or height for the vertical rise 76 is one-eighth inch.

Channel 70 includes the upper face 80, lower face 81 and bottom face 83. The upper face 80 extends into side wall 74 a shorter distance than the lower face 81, thereby giving a slope to the bottom face 83. The greater depth of the channel at the lower end relative to the upper end provides greater volume for mercury seeking this level because of what is believed to be the effect of gravity on the mercury. The sloping bottom wall thus reduces the possibility of the mercury extending out of the channel into the path of the sand.

The presently preferred dimensions for the embodiment of FIG. 3 when incorporated into the aforedescribed 36 inch bowl are: approximately one-eighth inch for the upper face 80, approximately three-sixteenths inch for the bottom face 81, and a distance between these faces of approximately 4 inches. The difference in depth between the upper and lower faces imparts the desired slope to the bottom face relative to the vertical. The radius defines the curve of the inner surface of the bottom wall and consequently the tangent point 71 between the vertical side wall and rounded bottom wall.

In both embodiments, erosion of the mercury, either by failure to deflect the material in a vertical path or by overfeeding the bowl with water and sand, will result in a gradual buildup of heavy sand below the rim 54 which soon extends downwardly and makes a solid cover over the mercury face, thus preventing; penetration of value particles into the mercury. Regardless of the size of bowl utilized, it has been found that maintaining the centrifugal force at approximately l,ll2 pounds per square inch provides for optimum recovery. This force, of course, will be regulated by the: speed of the shaft in relation to the diameter of bowl and the vertical depth of the mercury channel to be stabilized.

As the value-bearing material passes vertically parallel to the face of the mercury screen, the heavier particles of gold and platinum will be driven through the mercury screen and will build up on the face 58 of the channel displacing the mercury in the channel. As the values build up, the mercury will be caused to flow out of the bowl and will be recovered in the mercury trap 19. The values are recovered by cutting off the flow of water and sand and stopping the bowl to allow the power-like particles and mercury to fall to the bottom of the bowl. Some of the free gold particles, of course, will amalgamate with whatever mercury is present when the bowl is stopped.

From the foregoing, it will be apparent to those skilled in the art that the present invention provides significant improvements in centrifugal bowl separators and in methods of recovering values with the use of centrifugal force. Utilizing the stabilized mercury screen and the bowl configuration shown and with the method described, it is possible to recover microscopic, flour and flake gold and platinum particles heretofore impossible to separate by amalgamation or by centrifugal force. The arrangement and types of structural components utilized within this invention may be subject to numerous modifications well within the purview of the invention and applicant intends to be limited only to a liberal interpretation of the specification.

The embodiments of the invention which an exclusive property or privilege is claimed are defined as follows:

1. A centrifugal separator bowl used in recovering ore values having a higher specific gravity than mercury by causing them to pass through a screen of mercury by centrifugal force, the bowl adapted for rotation about a vertical axis comprising,

a vertical side wall and a bottom wall rounded upwardly with the inner surface of the bottom wall terminating at its point of tangency with the inner surface of the side wall, and

a continuous annular retention channel formed in the inside surface of said wall and positioned above said tangent point between the bottom and side walls providing a vertical rise portion on the inner face of the side wall having a height not greater than three-sixteenths inch and wherein the depth of said retention channel is greatest at the lower end thereof, whereby erosion of mercury in said channel by a mixture of values containing ore and water directed upwardly pass said mercury during rotation of said bowl is prevented.

2. The separator bowl of claim 1 wherein said retention channel includes horizontal upper and lower faces and a bottom face therebetween with the lower face extending into said side wall a greater distance than said upper face thereby imparting a slope relative to the vertical to said bottom face.

3. A centrifugal separator bowl for use in recovering ore values having a higher specific gravity than mercury by causing them to pass through a screen of mercury by its centrifugal force and adapted for rotation about a vertical axis comprising,

a vertical side wall and a bottom wall rounded upwardly with the inner surface of the bottom wall terminating at its point of tangency with the inner surface of the side wall,

a continuous angular retention channel formed in the a plurality of perforations in the center section adjacent said peripheral edge whereby a mixture of value-containing material and water introduced into said pan will be distributed on the bottom of the bowl. 

1. A centrifugal separator bowl used in recovering ore values having a higher specific gravity than mercury by causing them to pass through a screen of mercury by centrifugal force, the bowl adapted for rotation about a vertical axis comprising, a vertical side wall and a bottom wall rounded upwardly with the inner surface of the bottom wall terminating at its point of tangency with the inner surface of the side wall, and a continuous annular retention channel formed in the inside surface of said wall and positioned above said tangent point between the bottom and side walls providing a vertical rise portion on the inner face of the side wall having a height not greater than three-sixteenths inch and wherein the depth of said retention channel is greatest at the lower end thereof, whereby erosion of mercury in said channel by a mixture of values containing ore and water directed upwardly pass said mercury during rotation of said bowl is prevented.
 2. The separator bowl of claim 1 wherein said retention channel includes horizontal upper and lower faces and a bottom face therebetween with the lower face extending into said side wall a greater distance than said upper face thereby imparting a slope relative to the vertical to said bottom face.
 3. A centrifugal separator bowl for use in recovering ore values having a higher specific gravity than mercury by causing them to pass through a screen of mercury by its centrifugal force and adapted for rotation about a vertical axis comprising, a vertical side wall and a bottom wall rounded upwardly with the inner surface of the bottom wall terminating at its point of tangency with the inner surface of the side wall, a continuous angular retention channel formed in the inside surface of said side wall and positioned above said tangent point between the bottom and side walls providing a vertical rise portion on the inner face of the side wall having a height not greater than three-sixteenths inch, a stationary distributor pan located within said bowl having a conical center section and a vertically-directed flange extending from thE peripheral edge thereof, and a plurality of perforations in the center section adjacent said peripheral edge whereby a mixture of value-containing material and water introduced into said pan will be distributed on the bottom of the bowl. 